The immune systems of laboratory mice - the dominant animal model used in biomedical research - are more similar to the immature immune systems of newborn humans than to those of human adults, reports a paper published in Nature this week. Housing lab mice, which live in abnormally hygienic environments, with ‘dirty’ mice from pet stores could help to create an improved mouse model for translating research of many different diseases, the study suggests.

Studies in mice have provided important information about the role of the immune system in health and disease by enabling experimental techniques that are not technically or ethically possible in humans. Many therapies developed in mice, however, are unsuccessful in humans.

David Masopust and colleagues investigated the effect of the pathogen-free environment in which lab mice are housed on the composition of the immune system and its response to infection. They first found significantly fewer CD8+ T cells in traditional lab mice compared to premenopausal adult women. The authors then looked at the populations of these cells in free-living feral mice and mice from commercial pet stores and confirm that these differences are unique to lab mice. Co-housing pet store mice, which are not raised in extreme hygienic conditions, with the lab mice led to extensive changes in the immune cell lineages of the lab mice such that they came to resemble the immune signatures of adult humans. Compared to lab mice, pet store and co-housed mice had a more than 10,000-fold improved response to a bacterial infection, which matched the response of control lab mice that were previously vaccinated against the infection.

The authors explain that their study does not advocate the end of studies with lab mice. Instead, they argue that supplementing current mouse models with ‘dirty’ mice, such as feral animals or those from pet stores, has the potential to improve the translation of findings from mice to humans.